WA town of Collie remains on flood watch

Flood warnings remain in place for the town of Collie in Western Australia's south as residents mop up after Wednesday's deluge.

More than 127mm of rain fell on Collie, while downpours at nearby Yourdamung Lake have nudged 190mm.

Flash flooding inundated many Collie buildings on Wednesday, and sandbagging efforts continued on Thursday as more storms were forecast.

The Bureau of Meteorology warned that a line of thunderstorms could be seen on the radar stretching from Bunbury in the South West region to Pingelly in the Wheatbelt region.

"If you live between Lancelin to Northam to Narrogin to Mount Barker to Windy Harbour including Perth, Mandurah, Bunbury, Busselton, Margaret River and Bridgetown, you should take action and stay safe with thunderstorms or heavy rain," the Department of Fire and Emergency Services said.

"This does not include Narrogin or areas in the South Coastal district.

"This weather is unusual for this time of year and rainfall amounts are well above normal in some areas."